Electrostatic chuck

ABSTRACT

In accordance with an embodiment of the invention, there is provided an electrostatic chuck comprising an electrode, and a surface layer activated by a voltage in the electrode to form an electric charge to electrostatically clamp a substrate to the electrostatic chuck. The surface layer includes a plurality of protrusions extending to a height above portions of the surface layer surrounding the protrusions to support the substrate upon the protrusions during electrostatic clamping of the substrate. The protrusions are substantially equally spaced across the surface layer as measured by a center to center distance between pairs of neighboring protrusions.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/054,259, entitled “Electrostatic Chuck,” filed on May 19, 2008, andU.S. Provisional Application No. 61/094,700, entitled “ElectrostaticChuck,” filed on Sep. 5, 2008. The entire teachings of theseapplications are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

An electrostatic chuck holds and supports a substrate during amanufacturing process and also removes heat from the substrate withoutmechanically clamping the substrate. During use of an electrostaticchuck, the back side of a substrate, such as a semiconductor wafer, isheld to the face of the electrostatic chuck by an electrostatic force.The substrate is separated from one or more electrodes in the face ofthe electrostatic chuck by a surface layer of material that covers theelectrode. In a Coulombic chuck, the surface layer is electricallyinsulating, while in a Johnsen-Rahbek electrostatic chuck, the surfacelayer is weakly conducting. The surface layer of the electrostatic chuckmay be flat or may have one or more protrusions, projections or othersurface features that further separate the back side of the substratefrom the covered electrode. Heat delivered to the substrate duringprocessing can be transferred away from the substrate and to theelectrostatic chuck by contact heat conduction with the protrusionsand/or by gas heat conduction with a cooling gas. Contact heatconduction is generally more efficient than gas heat conduction inremoving heat from the substrate. However, controlling the amount ofcontact between the substrate and the protrusions can be difficult.

In microelectronics production, as semiconductor and memory devicegeometries become progressively smaller and the sizes of wafers, flatscreen displays, reticles and other processed substrates becomeprogressively larger, the allowable particulate contamination processspecifications become more restrictive. The effect of particles onelectrostatic chucks is of particular concern because the wafersphysically contact or mount to the chuck clamping surface. If themounting surface of the electrostatic chuck allows any particulate tobecome entrapped between the mounting surface and the substrate, thesubstrate may be deformed by the entrapped particle. For example, if theback side of a wafer is clamped electrostatically against a flatreference surface, the entrapped particle could cause a deformation ofthe front side of the wafer, which will therefore not lie in a flatplane. According to U.S. Pat. No. 6,835,415, studies have shown that a10-micron particle on a flat electrostatic chuck can displace thesurface of a reticle (i.e., a test wafer) for a radial distance of oneinch or more. The actual height and diameter of the particle-induceddisplacement is dependent on numerous parameters such as the particlesize, the particle hardness, the clamping force and the reticlethickness.

During substrate processing it is important to be able to control thetemperature of the substrate, limit the maximum temperature rise of thesubstrate, maintain temperature uniformity over the substrate surface,or any combination of these. If there are excessive temperaturevariations across the substrate surface due to poor and/or non-uniformheat transfer, the substrate can become distorted and process chemistrycan be affected. The greater the area of direct contact with theelectrostatic chuck, the greater the heat transferred by contact heatconduction. The size of the area of direct contact is a function of theroughness, flatness and hardness of the contact surfaces of thesubstrate and electrostatic chuck, as well as of the applied pressurebetween the contact surfaces. Since the characteristics of the contactsurface vary from substrate to substrate, and since the characteristicsof the contact surface can change over time, accurately controllingcontact heat conductance between the electrostatic chuck and substrateis difficult.

Controlling the temperature of a substrate and the number of particleson its back side is important for reducing or eliminating damage tomicroelectronic devices, reticle masks and other such structures, andfor reducing or minimizing manufacturing yield loss. The abrasiveproperties of the electrostatic chuck protrusions, the high contact areaof roughened protrusions, and the effect of lapping and polishingoperations during manufacture of electrostatic chucks may all contributeadder particles to the back side of substrates during use with anelectrostatic chuck.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, there is provided anelectrostatic chuck comprising an electrode, and a surface layeractivated by a voltage in the electrode to form an electric charge toelectrostatically clamp a substrate to the electrostatic chuck. Thesurface layer includes a plurality of protrusions extending to a heightabove portions of the surface layer surrounding the protrusions tosupport the substrate upon the protrusions during electrostatic clampingof the substrate. The protrusions are substantially equally spacedacross the surface layer as measured by a center to center distancebetween pairs of neighboring protrusions.

In further, related embodiments, the protrusions may be arranged in atrigonal pattern. At least one of the height and a contact area androughness of the protrusions may be such that at least one of thetemperature and the temperature distribution of the substrate, when thesubstrate is heated during the electrostatic clamping, is substantiallycontrolled by gas heat conduction of a gas in a space between thesubstrate, the protrusions, and the portions of the surface layersurrounding the protrusions. Greater than about 25%, or greater thanabout 50%, or greater than about 75%, of a top area of each of theprotrusions may contact the substrate during the electrostatic clamping.Less than about 5000 particle adders, or less than about 3000 particleadders, or less than about 2500 particle adders, or less than about 1500particle adders, may be deposited on a back side of the substrate as aresult of a use of the electrostatic chuck that includes at least oneof: the electrostatic clamping of the substrate, de-clamping thesubstrate from the electrostatic clamping, and performing theelectrostatic clamping during a manufacturing process performed on thesubstrate.

In other related embodiments, the protrusions may be formed from atleast one low stress material, which may comprise at least one of anamorphous dielectric material and a polycrystalline dielectric material.The protrusions may comprise a dielectric material having a resistivitygreater than about 10¹² ohm-cm. The dielectric material may included atleast one of silicon, an alloy of silicon with at least one otherelement, silicon carbide and non-stoichiometric silicon carbide.Further, the protrusions may comprise a dielectric material including atleast one of alumina and aluminum nitride. The protrusions may comprisea dielectric material such that a Johnsen-Rahbek force or partial hybridJohnsen-Rahbek force does not act on the substrate during theelectrostatic clamping. Also, the protrusions may comprise a compliantdielectric material; and may comprise a dielectric material having aresistivity such that the substrate is retained upon the electrostaticchuck via the Johnsen-Rahbek effect during the electrostatic clamping.

In further, related embodiments, a contact area of the protrusions withthe substrate may comprise from about 1% to about 10% of a total area ofthe electrostatic chuck. The protrusions may have a diameter of fromabout 0.75 millimeters to about 1 millimeter. The center to centerdistance between pairs of neighboring protrusions may be less than about8 millimeters, or less than about 6 millimeters, or less than about 4millimeters, or less than about 2 millimeters. The protrusions maycomprise at least one partial protrusion, the partial protrusioncomprising at least part of a surface structure of the electrostaticchuck, which may be selected from at least one of a gas channel, a liftpin and a ground pin. The height of the protrusions may be substantiallyequal to the mean free path of a gas located during the electrostaticclamping in a space between the substrate, the protrusions, and theportions of the surface layer surrounding the protrusions.

In other related embodiments, the protrusions may include a top surfacehaving a surface roughness metric reduced, by virtue of at least somemachine polishing, by between about 25% and about 75%, or by about 50%,by comparison with similar protrusions polished only by hand. Theprotrusions may include modified edge geometry produced by at least somemachine polishing, such that a characteristic rounding height of aprotrusion is shorter by comparison with a corresponding height of asimilar protrusion polished only by hand and such that a characteristicrounding length is longer by comparison with a corresponding length of asimilar protrusion polished only by hand. The ratio of thecharacteristic rounding height to the characteristic rounding length maybe reduced by a factor of between about 2 and about 5, or between about3 and about 4, by comparison with the similar protrusion polished onlyby hand. Less than about 5000 particle adders, or less than about 2000particle adders, of particle size range of 0.16 μm or greater may bedeposited on the back side of the substrate as a result of the use ofthe electrostatic chuck. Further, the protrusions may include modifiededge geometry such that a ratio of a characteristic rounding height of aprotrusion to a characteristic rounding length is between about 0.00407and about 0.00306, or between about 0.00611 and about 0.002444.

In a further embodiment according to the invention, the surface layer ofthe electrostatic chuck may comprise a charge control surface layer. Thecharge control surface layer may have a surface resistivity in the rangeof from about 1×10⁸ ohms/square to about 1×10¹¹ ohms/square; and maycomprise a silicon carbide composition. The surface resistivity of thecharge control surface layer may be controlled by varying the amount ofsilicon precursor gas and carbon precursor gas used to make the siliconcarbide composition. The silicon carbide composition may comprisesilicon carbide or non-stoichiometric silicon carbide. The chargecontrol surface layer may comprise at least one protrusion and a surfacecoating layer. The charge control surface layer may be formed by blanketdepositing a silicon carbide composition layer on a dielectric;patterning the silicon carbide composition layer using photolithography;and removing portions of the silicon carbide composition layer usingreactive ion etching to leave at least one silicon carbide compositionprotrusion. The charge control surface layer may also be formed bypatterning a dielectric layer using bead blasting or etching; andconformally coating the dielectric layer with the charge control surfacelayer. The charge control surface layer may comprise at least onematerial selected from the group consisting of diamond-like carbon,amorphous silicon, metal-doped oxide and combinations of these.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

FIG. 1 is a cross-sectional side view of a substrate bowing betweenprotrusions on the surface of an electrostatic chuck, in accordance withthe prior art.

FIG. 2 is a cross-sectional view of an electrostatic chuck according toan embodiment of the invention.

FIG. 3 is a cross-sectional view of a first layer and a dielectric layerof an electrostatic chuck according to an embodiment of the invention.

FIG. 4 is a profilometer map of a contoured dielectric protrusion on thesurface of an electrostatic chuck, in accordance with an embodiment ofthe invention.

FIG. 5A is an illustration of a pattern of protrusions on the surface ofan electrostatic chuck, in accordance with an embodiment of theinvention.

FIG. 5B is a shaded schematic diagram illustrating uniform loading of aprotrusion on an electrostatic chuck, as in an embodiment according tothe invention, as compared with edge loading of a protrusion, as in theprior art.

FIG. 6 is a graph of calculated force between a wafer and electrostaticchuck protrusions for various protrusion diameters and center to centerbump spacing, in accordance with an embodiment of the invention.

FIG. 7 is a graph of calculated contact area for different protrusiondiameters and center to center protrusion spacings, in accordance withan embodiment of the invention.

FIG. 8 is a diagram of protrusions on an electrostatic chuck featuring a4 millimeter center to center spacing and a diameter of 0.75millimeters, in accordance with an embodiment of the invention.

FIGS. 9A and 9B are graphs of a cross-sectional profile of a protrusionon an electrostatic chuck with and without (FIGS. 9A and 9Brespectively) an added stage of pad polishing, in accordance with anembodiment of the invention.

FIGS. 10A and 10B are close-up graphs of the cross-sectional profiles ofthe protrusions of FIGS. 9A and 9B, respectively, in accordance with anembodiment of the invention.

FIG. 11 shows an electrostatic chuck that includes a charge controlsurface layer, according to an embodiment of the invention.

FIG. 12 shows the surface pattern used for the protrusions in theelectrostatic chuck of the embodiment of FIG. 11.

FIG. 13 is a schematic cross-sectional view of the substrate contactsurface of the embodiment of FIG. 11.

FIG. 14 shows an alternative version of the coating for theelectrostatic chuck of FIG. 11 in which a conformal coating of chargecontrol material is used, in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

The inventors have recognized that the uneven loading of force between asubstrate and protrusions of an electrostatic chuck during electrostaticchucking is a source of particles that can be deposited on the back sideof the substrate as a result of use or during use of the chuck. Unevenloading of the substrate on the protrusions during chucking can alsolead to inconsistent contact heat conductance between the substrate andelectrostatic chuck. The uneven loading of the force between thesubstrate and protrusions can result when the substrate lifts near thecenter of the protrusion and/or bows between the protrusions, which canresult in the force between the substrate and the electrostatic chuckbeing distributed over the outer edge regions of the protrusions ratherthan across their surfaces. In some cases the uneven loading results inless than the full area of the protrusion contacting the substrate,which can result in a high concentration of force on a smaller area ofthe protrusions.

The uneven loading of the force between the substrate and theprotrusions as a result of use or during use of an electrostatic chuckcan result in particles that correlate with the protrusions. Inaccordance with an embodiment of the invention, these particles can bereduced or eliminated by distributing the force between theelectrostatic chuck and substrate across the area of the protrusions andby a substantially equal spacing of the protrusions across the surfaceof the chuck. In an electrostatic chuck according to an embodiment ofthe invention, the protrusions can have a height, contact area, androughness such that gas heat conduction controls the substratetemperature and the temperature distribution of the substrate. Inaccordance with an embodiment of the invention, greater than 25% of thearea of each protrusion may contact the substrate during chucking.Further, the number of particles on the back side of the substrate fromthe uneven loading between the substrate and the protrusions may be lessthan 5,000 adders, and in some case less than 3,000 adders, and infurther cases less than 2,500 adders, and in still other cases less than1,500 adders. Lower numbers of particles indicate more uniformdistribution of substrate loading, less wafer lift at the center of theprotrusion, less wafer bowing between protrusions, and lower contactforces between protrusions and the substrate, which results in fewerparticles correlated with the protrusions. The lower the number of suchparticles, the lower the number of manufacturing defects, the better thegas seal for the electrostatic chuck, and the higher the manufacturingyield.

In accordance with an embodiment of the invention, an electrostaticchuck is provided with a surface having substantially equally spacedprotrusions across the surface of the electrostatic chuck that contactthe back side of the chucked substrate. The spacing, height, and contactarea of the protrusions are so arranged as to provide an acceptabletemperature and temperature uniformity during a process that treats thesubstrate. The arrangement of protrusions provides a force between thesubstrate and the electrostatic chuck that holds the substrate anddistributes the force across the protrusions so that, for example, fewerthan 3,000 particles correlated with the protrusions are added to theback side of the substrate from the force or contact. The protrusionsare made from a low stress material that reduces the number of particlescaused by stress cracks or fractures, and can reduce gas leaks throughthe electrostatic chuck gas seals. The arrangement of the electrostaticchuck protrusions may reduce or eliminate the uneven loading of thesubstrate against the protrusions, and may reduce particles, providebetter temperature control and uniformity across the substrate, or anycombination including these.

In accordance with an embodiment of the invention, an electrostaticchuck provides more uniform loading of the substrate with theprotrusions, by featuring a plurality of protrusions formed across theface of the electrostatic chuck, the protrusions or a portion of thembeing equally spaced across the surface of the electrostatic chuck. Forexample, the protrusions may be arranged in a pattern such as a trigonalpattern. The contact area of the protrusions may range from greater than1% to less than about 10% of the electrostatic chuck area. Theprotrusions may be arranged to have a diameter of from 0.75 millimetersto 1 millimeter, and may be substantially equally spaced apart by adistance of less than 8 millimeters. A wafer held by such anelectrostatic chuck may be retained substantially without bowing in theregions between the protrusions and without lifting in the center of theprotrusions, thereby avoiding the production of undesirable particles.An embodiment according to the invention reduces or eliminates particleson the back side of the substrate that correlate with the protrusions,and provides a substantially uniform temperature and temperature rangeor distribution across the substrate.

In accordance with an embodiment of the invention, particles added tothe back side of a substrate as a result of the uneven loading of forcebetween the substrate and the surface of an electrostatic chuck can bereduced or eliminated by an equally spacing, or substantially equallyspacing, protrusions across the surface of the electrostatic chuck forcontacting the back side of the substrate. The spacing and contact areaof the protrusions on the electrostatic chuck are so arranged as toprovide acceptable heat removal from the substrate during amanufacturing process. Further, the spacing and contact area of theprotrusions provide a force between the substrate and the electrostaticchuck that holds the wafer without causing substrate bowing between theprotrusions, and that distributes the load across the protrusions,thereby reducing the number of particles correlated with the protrusionson the back side of the substrate.

FIG. 1 is a cross-sectional side view of a substrate 100 bowing betweenprotrusions 101, 102 on the surface 103 of an electrostatic chuck 104,in accordance with the prior art. Under the pressure of electrostaticforce 105, the substrate 100 bows downwards in regions 106 between theprotrusions 101, 102, and lifts in the center regions 107 of theprotrusions 101, 102. (The extent of bowing and lifting is exaggeratedin FIG. 1 for purposes of illustration). As a result of the bowing andlifting of the substrate 100, high contact forces can be generatedbetween the substrate 100 and the edges 108, 109 of the protrusions,which can create local areas of stress and create undesirable particles,the location of which may correlate with the locations and/or featuresof the protrusions 101, 102 on the electrostatic chuck. As illustratedin FIG. 1, during chucking, bowing of the substrate 100 betweenprotrusions 101, 102 and possible lifting of the substrate at the center107 of the protrusions 101, 102 can lead to uneven loading on theprotrusions 101, 102 and particles on the back side of the substrate.

By contrast, in accordance with an embodiment of the invention, equallyspaced protrusions that contact the back side of the electrostaticallychucked substrate may reduce particulate contamination that correlateswith the protrusions on the substrate back side, may produce uniformtemperature across the substrate, and may produce a strong chuckingforce. The area of any protrusion in contact with the back side of thesubstrate can be chosen to reduce or eliminate substrate lift at one ormore of the protrusions, reduce or eliminate substrate bowing betweenprotrusions, provide a more even loading of substrate force on theprotrusions, and reduce particles that correlate with the protrusionsdue to uneven substrate protrusion loading. In one embodiment accordingto the invention, greater than 25% of the area of each protrusioncontacts the substrate during chucking; in another embodiment, greaterthan 50% of the area of each protrusion contacts the substrate duringchucking; and in a further embodiment of the invention, greater than 75%of the area of each protrusion contacts the substrate during chucking.The amount of protrusion contact area can be determined by the flatnessof the substrate during a process, by a decrease in substrate back sideparticles correlated with the protrusions, or by a marking between atest substrate and a transferable marking material on the protrusions.In one embodiment, protrusions are substantially cylindrical and have adiameter on the top surface that can be in the range of from greaterthan 0.5 millimeters to less than 1.5 millimeters. Other shapedprotrusions with an area similar to these can also be used.

In accordance with an embodiment of the invention, the protrusions orportions of them are spaced equally or substantially equally apartacross the electrostatic chuck surface and are above the electrode in adielectric layer. The spacing between protrusions can be measured fromthe center of the top of one protrusion to the center of the tops ofadjacent protrusions. The spacing can be in a regular pattern. Forexample, in one embodiment, the spacing of protrusions is in a trigonalpattern that reduces the force per unit area with the chucked wafer orother substrate by 20-30 percent compared to a square pattern ofprotrusions. In accordance with an embodiment of the invention, aprotrusion near a gas channel, lift pin, ground pin or other surfacestructure may differ from other protrusions by having a portion of theprotrusion formed as the surface structure and another portion extendingout from the surface structure as a partial protrusion. Alternatively,such a protrusion may have a smaller or larger size or a different shapethan other protrusions on the surface of the electrostatic chuck. Forexample, a cylindrically shaped protrusion near a gas seal may have aportion of the cylinder formed as the gas seal and another portionextending out from the gas seal. In addition, the location and size ofthe gas channels, lift pins, ground pins and other surface structuresmay be modified to provide uniform protrusion spacing; and protrusionsnear such surface structures may be spaced from them such that thespacing from a protrusion to a surface structure is the same as orsmaller than the spacing from protrusion to protrusion. In oneembodiment, the protrusion spacing may be less than 8 millimeters centerto center; in another embodiment the protrusion spacing may be about 6millimeters or less center to center; in another embodiment theprotrusion spacing is about 4 millimeters or less center to center; andin another embodiment the protrusion spacing is about 2 millimeters orless center to center, especially for small diameter protrusions ofabout 0.5 millimeters of less or equivalents thereof.

Generally, the amount of contact area between the protrusions and thesubstrate affects the amount of contact heat conduction from thesubstrate to the protrusions, and also affects the amount of bowing andlifting of the substrate during chucking. In accordance with anembodiment of the invention, the contact area of the protrusions withthe substrate, based on the geometric area of the protrusions and notincluding gas seals, can be in the range from greater than 1% to lessthan about 10% of the area of the electrostatic chuck's surface. Sincegas heat conduction with a cooling gas is easier to control than contactheat conduction, another embodiment of the invention has such a contactarea in the range of from greater than 1% to about 4%; and a furtherembodiment of the invention has such a contact area in the range of fromabout 2% to about 4%.

According to U.S. Pat. No. 6,117,246, one disadvantage of using anelectrostatic chuck body fabricated from a ceramic, which is adielectric, is that during manufacture of the support, the ceramicmaterial is “lapped” to produce a relatively smooth surface. Accordingto U.S. Pat. No. 6,117,246, such lapping produces particles that adhereto the surface of the support, and that are very difficult to completelyremove from the surface. Further, the lapping process may fracture thesurface of the chuck body. Consequently, as the chuck is used, particlesare continuously produced by these fractures. Also according to U.S.Pat. No. 6,117,246, during wafer processing, the ceramic material canabrade the wafer oxide from the underside of the wafer, resulting infurther introduction of particulate contaminants to the processenvironment. During use of the chuck or as a result of use of the chuck,the particles can adhere to the underside of the wafer and can becarried to other process chambers or cause defects in the circuitryfabricated upon the wafer. According to U.S. Pat. No. 6,117,246, tens ofthousands of contaminant particles may be found on the back side of agiven wafer after retention upon a ceramic electrostatic chuck.

By contrast, in accordance with an embodiment of the invention,protrusions are formed on an electrostatic chuck by processes thatresult in low stress materials, which resist cracking and resist changesin dimension, thereby minimizing particle sources and providing moreuniform loading of the substrate on the area of the protrusions. Forexample, protrusions may be formed of amorphous films made by PlasmaEnhanced Chemical Vapor Deposition (PECVD). The protrusions may beformed of a dielectric material, such as an amorphous dielectricmaterial or a polycrystalline dielectric material. The dielectricmaterial may be patterned by a process that provides a low stressmaterial, such as a reactive ion etching process, a chemical etchingprocess, or a bead blasting process. Stress may be measured in thedielectric by films deposited on a wafer and then characterized by waferbowing, X-ray diffraction or Raman Spectroscopy.

In accordance with an embodiment of the invention, the electrostaticchuck is a Coulombic chuck, and the dielectric for the Coulombic chuckmay have a resistivity greater than about 10¹² ohm-cm. The dielectricmay be silicon or an alloy of silicon with other elements, for examplesilicon carbide or non-stoichiometric silicon carbide compositions. Thedielectric can include aluminum, for example alumina or aluminumnitride. In a further embodiment according to the invention, theelectrostatic chuck is a Johnsen-Rahbek electrostatic chuck.Alternatively, the electrostatic chuck may not be a Johnsen-Rahbekelectrostatic chuck, and the dielectric may be chosen so that aJohnsen-Rahbek (JR) force or partial hybrid Johnsen-Rahbek force doesnot act on the wafer or substrate. One or more protrusions may include acompliant dielectric material, such as any of the suitable compliantmaterials disclosed in U.S. Pat. No. 6,835,415, the disclosure of whichis hereby incorporated herein by reference in its entirety. In oneembodiment according to the invention, the dielectric for theprotrusions is made from a silicon carbide film having a resistivity ofabout 10⁸ ohm-cm, or about 10¹⁰ ohm/sq, an internal compressive filmstress in a range of less than about 450 MPa, and more preferably lessthan about 450 MPa (as deposited). The layer of silicon carbidepreferably is deposited to a thickness in a range of about 2-10 microns.

In another embodiment according to the invention, the dielectric for theprotrusions is made from a charge control surface layer material havinga resistivity of from about 10⁸ ohm/sq to about 10¹¹ ohm/sq, an internalcompressive film stress of less than about 450 MPa, and more preferablyless than about 450 MPa (as deposited). The charge control layer may bedeposited to a thickness in a range of from about 0.1 to about 10microns thick, or preferably from about 1 to about 3 microns thick. Inaddition, the dielectric for the protrusions may be formed with a lowstress material (such as one with an internal compressive film stress ina range of less than about 450 MPa), and then overcoated with a thincoating of diamond-like carbon (or other material that typically has ahigher compressive film stress) to achieve the desired surfaceresistivity.

In another embodiment according to the invention, the dielectric may bea ceramic or polymeric material having a controlled resistivity within arange of about 10⁷-10¹² ohm-cm, which allows a wafer or other workpieceto be supported and retained upon the electrostatic chuck via theJohnsen-Rahbek effect.

In order to characterize an electrostatic chuck according to anembodiment of the invention, and to compare such electrostatic chuckswith each other, there may be used a technique of correlating particleproduction with protrusion locations. In general, during use of anelectrostatic chuck, undesirable particles can accumulate on theprotrusion and channel surfaces of the electrostatic chuck and/or theback side surface of the substrate. Such undesirable particles arereferred to herein as “adders” or “particle adders.” Particles can bemeasured and compared before and after use of the electrostatic chuck inprocessing or chucking/dechucking. A correlation technique may includeanalyzing the correlation between the locations of protrusions on theelectrostatic chuck and the locations where particles have been producedon the back side of the substrate. Based on the degree of correlationbetween the protrusion locations and the particle locations, it can bedetermined how evenly loaded is the electrostatic force between thesubstrate and the protrusions. An uneven loading of the electrostaticforce generally produces a closer correlation between the protrusionlocations and the particle locations, while a more even loading producesa lack of correlation. The correlation technique may include correlatingthe location of the protrusions, or of features of the protrusions,with: the location of particles; the number and size of particles; thedistribution of particle sizes; the particle composition, or anycombination of these. Particles that correlate with the protrusions canbe detected by laser surface scanning of the substrate and theelectrostatic chuck, and determination of the number, size, anddistribution of the particles added after processing orchucking/dechucking. Repeated processing (etching, ion implantation, andthe like), repeated chucking and dechucking of the substrate (forexample, performing one million chuck/release cycles), pop off testing,and other simulated processing acts can be used to evaluate the numberof particle adders for an electrostatic chuck.

In accordance with an embodiment of the invention, the number ofparticles on the back side of a substrate that correlate withelectrostatic chuck protrusions, the particles having been produced byuneven loading of force between the substrate and the protrusions, maybe less than 5000, in some cases less than 3,000, in further cases lessthan 2,500, and in still other cases less than 1,500 for a 300millimeter diameter wafer after clamping in vacuum for 60 secondswithout cooling gas. For substrates having larger or smaller surfaceareas, for example 450 mm or 200 mm wafers, the number of particleadders can be scaled according to the substrate area. Lower numbers ofparticles indicate a more uniform loading of forces between thesubstrate and protrusions. A more uniform loading of force produces lesssubstrate lift at the center of the protrusion, less substrate bowingbetween protrusions, lower contact forces between protrusion edges andthe substrate, and more consistent heat transfer. The lower the numberof back side particles on the substrate that correlate with theprotrusions, the lower the number of manufacturing defects and thehigher the manufacturing yield.

In one embodiment according to the invention, there is a reduced totalback side loading of particles that correlate with protrusions as aresult of the uneven loading of force, per wafer clamp between anelectrostatically chucked wafer or substrate and electrostatic chucksurface protrusions. The size and distribution of the back sideparticles may, for example, be as follows: for 0.12 to 0.16 micronparticle size, less than 800 adders; for 0.16 to 0.2 micron particlesize, less than 500 adders; for 0.2 to 0.3 micron particle size, lessthan 500 adders; for 0.300 to 0.5 micron particle size, less than 500adders; for 0.5 to 1.0 micron particle size, less than 175 adders; for 1to 2 micron particle size, less than 100 adders; for 2 to 5 micronparticle size, less than 50 adders; for 5 to 10 micron particle size,less than 20 adders; or a total of less than 2645 adder particles acrossthese particle size ranges that correlate with the protrusions for a 300millimeter diameter wafer after clamping in vacuum for 60 secondswithout cooling gas. In accordance with an embodiment of the invention,the total number of adder particles may be less than the total sum ofone or more of these size ranges. For example, for particles between 0.5and 10 microns, an embodiment may have the following distribution ofparticles: for 0.5 to 1.0 micron particle size, less than 175 adders;for 1 to 2 micron particle size, less than 100 adders; for 2 to 5 micronparticle size, less than 50 adders; for 5 to 10 micron particle size,less than 20 adders; or a total of less than 345 adder particles acrossthese particle size ranges that correlate with the protrusions for a 300millimeter diameter wafer after clamping in vacuum for 60 secondswithout cooling gas.

In another example, the distribution may be as follows: for 0.12 to 0.16micron particle size, less than 600 adders; for 0.16 to 0.2 micronparticle size, less than 275 adders; for 0.2 to 0.3 micron size, lessthan 325 adders; for 0.300 to 0.5 micron particle size, less than 450adders; for 0.5 to 1.0 micron, particle size less than 300 adders; for 1to 2 micron particle size, less than 120 adders; for 2 to 5 micronparticle size, less than 30 adders; for 5 to 10 micron particle size,less than 10 adders; or a total of less than 2110 adders across theseparticle size ranges for a 300 millimeter diameter wafer after clampingin vacuum for 60 seconds without cooling gas. In accordance with anembodiment of the invention, the total number of adder particles may beless than the total sum of one or more of these size ranges. Forexample, for particles between 0.3 and 10 microns, an embodiment mayhave the following distribution of particles: for 0.300 to 0.5 micronparticle size, less than 450 adders; for 0.5 to 1.0 micron particlesize, less than 300 adders; for 1 to 2 micron particle size, less than120 adders; for 2 to 5 micron particle size, less than 30 adders; for 5to 10 micron particle size, less than 10 adders; or a total of less than910 adder particles across these particle size ranges that correlatewith the protrusions for a 300 millimeter diameter wafer after clampingin vacuum for 60 seconds without cooling gas. Other sizes anddistributions of back side particles may be obtained; for example, lessthan about 5000 adder particles of a diameter greater than 0.16 micronsmay be obtained; or less than about 5000 adder particles of a diametergreater than 0.12 microns may be obtained.

In a further embodiment according to the invention, the surface layer ofthe electrostatic chuck may comprise a charge control surface layer. Thecharge control surface layer may have a surface resistivity in the rangeof from about 1×10⁸ ohms/square to about 1×10¹¹ ohms/square; and maycomprise a silicon carbide composition. The surface resistivity of thecharge control surface layer may be controlled by varying the amount ofsilicon precursor gas and carbon precursor gas used to make the siliconcarbide composition. The silicon carbide composition may comprisesilicon carbide or non-stoichiometric silicon carbide. The chargecontrol surface layer may comprise at least one protrusion and a surfacecoating layer. The charge control surface layer may be formed by blanketdepositing a silicon carbide composition layer on a dielectric;patterning the silicon carbide composition layer using photolithography;and removing portions of the silicon carbide composition layer usingreactive ion etching to leave at least one silicon carbide compositionprotrusion. The charge control surface layer may also be formed bypatterning a dielectric layer using bead blasting or etching; andconformally coating the dielectric layer with the charge control surfacelayer. The charge control surface layer may comprise at least onematerial selected from the group consisting of diamond-like carbon,amorphous silicon, metal-doped oxide and combinations of these.

In the art of electrostatic chucks, protrusions on the electrostaticchuck that contact the back side of the substrate can be referred to asmesas, bumps, pins, islands, surface structures and the like. Inaccordance with an embodiment of the invention, protrusions on anelectrostatic chuck may have a size, spacing, and composition thatallows the maintaining of a substantially uniform pressure across thesurface of the substrate, and of a substantially uniform distribution ofthe force between the protrusions and the substrate. FIG. 2 is across-sectional view of an electrostatic chuck 204 according to anembodiment of the invention. The top surface of protrusions 201 contactthe back side of a substrate 200, and by their support of the substrate200, provide uniform loading and reduced levels of particles correlatedwith the projections 201. The protrusions 201 have side walls 210, andare separated by gaps 211. The electrostatic chuck 204 includes adielectric layer 212 that may have protrusions 201 formed in it.Alternatively, the protrusions 201 may be formed in one or more layersof material disposed on the surface of the dielectric layer 212. One ormore electrodes 213 are formed in a first layer 214, which is covered bythe dielectric 212. Beneath the first layer 214 are a first adhesivelayer 215, a second layer 216, an optional second adhesive layer 217,and a bottom layer 218 that contacts a cooling fluid, such as water. Thedielectric layer 212 includes a gas seal annular ring 219 formed in itsperiphery. Process energy is received by the substrate as indicated byarrow 220; and energy is removed as indicated by arrow 221.

FIG. 3 is a cross-sectional view of a first layer 314 and a dielectriclayer 312 of an electrostatic chuck 304 according to an embodiment ofthe invention. An electrode 313 in the first layer 314 is covered by thedielectric layer 312. In addition to a gas seal 319, the dielectriclayer 312 includes protrusions 301. The features and dimensions of theprotrusions 301 and dielectric layer 312 include a channel or gapsurface bottom 322, a gap spacing 323, a protrusion top surface 324, aprotrusion width or area 325, and a protrusion height 326.

In accordance with an embodiment of the invention, protrusions may beany regularly or irregularly shaped three dimensional solid or cavity,and may be disposed in any regular geometric or other pattern thatsubstantially equally distributes force to the substrate and reducesparticles due to uneven loading between the substrate and protrusions.Each protrusion may have a cylindrical side or a plurality of sides anda top. The edges of the protrusions may be square, as in the embodimentof FIG. 2, or may be contoured to help distribute the load between thesubstrate and chuck.

FIG. 4 is a profilometer map of a contoured dielectric protrusion on thesurface of an electrostatic chuck, in accordance with an embodiment ofthe invention. The protrusion has a contour with rounded edges, whichmay be formed, for example, by mechanical polishing. In the embodimentof FIG. 4, the protrusion has a diameter of about 500 μm and a height ofabout 6 μm, although other dimensions may be used.

FIG. 5A is an illustration of a pattern of protrusions 501 on thesurface of an electrostatic chuck, in accordance with an embodiment ofthe invention, in which the protrusion pattern is used to reduce theforces between a substrate and the protrusions 501. Protrusion patternsthat equally distribute such forces may be used, for example trigonal orgenerally hexagonal patterns of protrusions. It should be appreciatedthat, as used herein, a “trigonal” pattern is intended to mean aregularly repeating pattern of equilateral triangles of protrusions,such that the protrusions are substantially equally spaced apart. (Sucha pattern may also be viewed as being generally hexagonal in shape, witha central protrusion in the center of an array of six protrusions thatform the vertices of a regular hexagon). Forces may also be reduced byincreasing the diameter 427 of the protrusions, or by decreasing thecenter-to-center spacing 428 of the protrusions 501. As shown in theembodiment of FIG. 5A, the protrusions may be disposed in an equallyspaced arrangement, in which each protrusion is substantially equallyspaced apart from the adjacent protrusions by a center to center spacingdimension 428. By virtue of such spacing, as shown in the embodiment ofFIG. 2, a substantial portion of the back side of the substrate contactsthe top portion of the protrusions, which may include surface roughnessnot shown, leaving a gap 211 between the protrusions for helium or othergas for back side cooling. By contrast, without such protrusion spacing,only a small portion, 10% or less, of the protrusions may contact thesubstrate. In accordance with an embodiment of the invention thesubstrate may contact greater than 25% of the protrusion's top surfacearea.

FIG. 5B illustrates the differences between uniform loading of aprotrusion (as in an embodiment according to the invention) and edgeloading of a protrusion (as in the prior art) on an electrostatic chuck.The shading illustrates the relative amount of loading, for both auniform loading and a 10% edge loading (not necessarily to scale).

In accordance with an embodiment of the invention, protrusions may beeither rough or polished, provided that the surface has a low stress.For example, protrusion surfaces may be polished, such as by mechanicalpolishing, to reduce high contact forces that occur on rough protrusionsurfaces. In accordance with an embodiment of the invention, protrusionsmay have a peak to valley roughness of 2 microns or less R_(a), in someversions 0.2 microns or less R_(a) Low surface roughness can provide amore uniform distribution of force across the substrate during chucking.The surface roughness may be modified by wet etching and/or blasting thesurface with abrasives or beads under conditions that do not increasestress, or lead to an increase in particles correlated with theprotrusions, as a result of the use of the electrostatic chuck. Suchcontrolling of the surface finish of an electrostatic chuck may be usedto control the contact regions of the protrusions with the substrate,and to control heat transfer due to physical contact between thesubstrate and protrusions. The amount of contact between roughenedsurfaces and the substrate can also be adjusted by the magnitude of theelectrostatic clamping voltage.

In general, semiconductor wafers, reticles, solar cells, and othersubstrates or workpieces may be supported by an electrostatic chuckduring use in various coating, etching, lithography, and implantationprocesses. Processes or uses can include chucking (attraction) anddechucking (release) of the substrate. Processes or uses can includethose that result in the addition or generation of heat. In someprocesses the substrate piece is held in a reduced pressure environmentin a vacuum chamber, for example during reactive ion-etching (RIE),plasma etching, ion-beam etching, etching, physical vapor deposition(PVD), chemical vapor deposition (CVD), or other processes. During use,or during a process, an electrostatic chuck may, for example, retain asubstrate in a chucking step; undergo a coating, implant or othertreatment; and then release the substrate in dechucking step. Thesesteps or acts may be repeated. In the fabrication of integratedcircuits, a number of processes also involve the application of ionbeams to semiconductor wafers in vacuum. These processes include, forexample, ion implantation, ion beam milling and reactive ion etching. Ineach instance, a beam of ions is generated in a source and isaccelerated toward a target substrate. One way to achieve highthroughput is to use a high current ion beam so that the implantationprocess is completed in a relatively short time. However, large amountsof heat are likely to be generated by the high current ion beam. Theheat may result in uncontrolled diffusion of impurities beyond describedlimits in the wafer and may result in degradation of patternedphotoresist layers.

An electrostatic chuck in accordance with an embodiment of the inventionmay provide acceptable heat removal from a substrate as a result of useof the electrostatic chuck during a process. Generally, in varioussemiconducting processes, heat is generated that is transferred to thesubstrate. In semiconductor manufacturing, the substrate may be asemiconductor wafer upon which a number of devices are fabricated at thesame time. This makes it desirable to maintain a specified temperatureand temperature range, or temperature distribution, across the waferduring the process. Acceptable heat removal results in a substantiallyuniform temperature and temperature range, or temperature distribution,across the wafer during the process. In accordance with an embodiment ofthe invention, the temperature distribution across the wafer may vary by±25° C. or less, for a substrate temperature that can be controlled toabout 400° C. or less, or in some cases to about 250° C. or less, or instill other cases to about 100° C. or less. In accordance with anembodiment of the invention, a process may result in a heat input to thesubstrate that may range from about 1 watt/cm² to about 8 watts/cm². Thetemperature and distribution of temperatures may be measured at variousdifferent locations across the substrate, and the temperaturedistribution across the wafer may vary by ±5° C. or less for a substratetemperature that can be controlled to about 100° C. or less, or in somecases to about 70° C. or less, or in still other cases to about 10° C.or less. In another embodiment according to the invention, the processmay result in a heat input to the substrate that may range from about0.1 watt/cm² to about 2 watts/cm². In an implant application inaccordance with an embodiment of the invention, the total heat load maybe up to about 1500 watts (˜2 w/cm²), the wafer temperature may rise toabout 70° C. from room temperature, and there may be a +/−15° C.temperature variation. Further embodiments of the electrostatic chuckaccording to the invention may be used with higher temperatureapplications, such as a 400° C. heated chuck in an etch application, orwith lower temperature applications, such as a room temperatureapplication with a highly controlled temperature (+/−0.01° C.).

Generally, during a process, electrostatic chucks dissipate most of theheat from a chucked substrate in two ways: first, by gas heat conductionthrough a cooling gas in a gap between the substrate and electrostaticchuck dielectric; and second, by contact heat conduction, which isconduction directly across the microscopic and macroscopic points (forexample protrusion roughness and protrusions respectively) of contactbetween surfaces at the substrate electrostatic chuck interface. Theoverall heat transfer coefficient of the electrostatic chuck is theseries sum of the reciprocal of the heat transfer coefficients for eachof the layers. If the area of the contact surfaces of the electrostaticchuck surface protrusions is increased it can become difficult tocontrol the temperature of the semiconductor wafer above 100° C. ormore, for example in a temperature range of 300° C. to 400° C. This isbecause the temperature of the semiconductor wafer largely decreasesthrough the contact heat conduction from the substrate to theprotrusions. The amount of heat transferred by contact heat conductionis determined by the size of the area of direct contact between contactsurfaces or protrusions of the chuck and the back side of the substrate.

In an electrostatic chuck, back side gas heat conduction is the transferof thermal energy between the substrate and chuck surface. Heat transfercan occur by conduction of heat by gas atoms or molecules between thebody of the chuck and the wafer. Back side gas conduction takes placewhen the molecules or atoms of the gas leave the back side of thesubstrate with heat energy and deliver that energy to the electrostaticchuck surface. According to U.S. Pat. No. 6,839,217, gas conduction heattransfer has the disadvantage that the area of the protrusions must bestrictly controlled dimensionally to match the characteristic distancesof the mean free path of the gas at the pressures of the gases used.Further according to U.S. Pat. No. 6,839,217, leakage of the gas can bea problem for vacuum processes and may result in non-uniform cooling andpossible degradation of the process by localized gas concentrations atthe leakage areas. For a given cooling capacity, the gas pressurebetween the substrate and electrostatic chuck may flex the wafer andpossibly degrade the integrity of the process and process yield.

In an electrostatic chuck according to an embodiment of the invention,the height of the protrusions is preferably approximately the same as,or substantially equal to, the mean free path of the gas used in backside cooling. For example, for a back side cooling gas at 10 torr (1333Pa), the mean free path is 5 microns and accordingly the height of theprotrusion should be 5 microns or about 5 microns. The mean free pathdepends upon gas pressure and the molecular diameter of the gas andtemperature to achieve the most efficient heat conduction. The height ofthe protrusions may be modified to take into account processtemperatures, pressure, back side gas pressure, and chucking force. Inone embodiment according to the invention, the height of the protrusionsis about 6 microns.

An electrostatic chuck according to an embodiment of the invention mayoptionally include gas inlets, gas channels and the like located acrossthe chuck and or towards the periphery of the chuck, to distributecooling gas to the underside of a substrate held by the chuck. The size,location, and shape of the channels and/or gas inlets distributes gas inthe gap, minimizes pressure gradients, and facilitates the transfer ofheat from the wafer to the chuck. The gas introduced into the spacesbetween the substrate and chuck provides thermal heat transfer tocontrol the wafer temperature. At the same time, the gas pressure (2-20torr) is low enough that the attractive or clamping force holding thesubstrate, 25-35 torr, is not seriously diminished. An electrostaticchuck according to an embodiment of the invention may include one ormore annular shaped rings as disclosed in U.S. Pat. No. 6,608,745, nearthe edge or outer periphery of the chuck. These rings can have a heightsimilar to the protrusions and a width sufficient to provide a gas sealbetween the substrate and ring edge. In some cases the amount of gasthat can by-pass the gas seal is less than 0.2 sccm for a gas pressurebetween the chuck and substrate at vacuum chamber pressures less that 1atmosphere.

An electrostatic chuck in accordance with an embodiment of the inventionof the invention can be used to hold a substrate in place byelectrostatic force. The substrate is separated from an electrode by aninsulating dielectric layer. One or more electrodes are formed withinthe dielectric and covered with a layer of the dielectric. A DC voltage(for a Coulombic chuck) can be applied to the electrodes to produceelectrostatic force which clamps the wafer to the chuck. In some casesan alternating current or RF power can be applied to the electrodes. (Analternating current may be applied, for example, at a frequency of 30 Hzor another frequency. When RF power is applied, which is typically onlyin a sputtering or etch system, the self-bias or DC-bias voltageprovides the chucking force). The voltage applied to the electrodeproduces an electrostatic charge on the contact surface of theinsulating layer of the electrostatic chuck, which produces an equal andopposite electrostatic charge on the contact surface of the substrate.The electrostatic charges on the contact surfaces of the electrostaticchuck and substrate produce an electrostatic force between them. Thiselectrostatic force holds the substrate against the electrostatic chuckdielectric layer and any protrusions on the electrostatic chuck. Heatdelivered to the substrate can be transferred by contact heat conductionand gas heat conduction to the insulating layer of the gap or channelsurface bottom of the electrostatic chuck which is cooled, typicallywith cooling water. In use, a substrate such as a wafer, supported onthree lift pins, is dropped down onto the protrusions of theelectrostatic chuck and then the power or voltage for the electrostaticchuck is turned on. Cooling gas, such as helium, is introduced from apressure controlled gas source through an array of gas inlets. The gasinlets may be connected by a manifold and hoses to a vacuum pump. Acentral gas inlet may also be used to allow the gas pressure toequilibrate beneath the wafer more rapidly. It can also speed up theremoval of the gas at the end of wafer processing when the wafer isabout to be removed from the chuck. Given the small gap between waferand chuck, additional gas ports may be needed for this purpose. Inoperation, the substrate is clamped to the chuck, valves are opened anda gas such as helium is introduced from gas inlet holes under thesurface of the substrate, which is supported by the protrusions of thechuck surface. At the end of processing, for example after ionimplantation has occurred, the valves are opened, the coolant gas ispumped out, the electrostatic chuck power is turned off, the lift pinsare raised, the effector is inserted and the substrate is removed fromthe chuck.

In accordance with an embodiment of the invention, an electrostaticchuck can include lift pins and ground pins. Gas sealing surfaces may beformed around these in a similar fashion to the annular gas seal ringnear the edge of the electrostatic chuck. Where possible, in accordancewith an embodiment of the invention, these gas sealing structures may beformed in such a way as to encourage the uniformity of the distributionof force between the substrate and chuck, for example by includingportions of protrusions as discussed above.

Substrates used with an electrostatic chuck according to an embodimentof the invention can include semiconductor wafers, flat screen displays,solar cells, reticles, photomasks, and the like that are held by theelectrostatic chuck. Regardless of the shape, the substrates can have anarea equal to or greater than a 100 millimeter diameter wafer, a 200millimeter diameter wafer, a 300 millimeter diameter wafer or a 450millimeter diameter wafer.

In general, electrostatic chucks utilize the attractive force, which issimilar to the force between two plates of a capacitor, to hold asubstrate, such as a wafer, in place. In accordance with an embodimentof the invention, this clamping force may be in the range of 25 to 35torr, including values within this range, such as 26 torr, 33 torr, andothers. If the wafer is separated from the chuck by an insulator ofdielectric constant ∈ and thickness d, and a voltage V is appliedbetween them, an attractive force F is generated between them asfollows:

$F = {\left( \frac{ɛ\; V^{2}}{2d^{2}} \right)A}$

where A is the common area of the wafer and chuck electrode. To obtain alarge attractive force for a given voltage, the distance d separatingthe wafer and the chuck electrode can be minimized by using a thindielectric layer. Therefore, in accordance with an embodiment of theinvention, in order to obtain a chucking force, the dielectric layer mayhave a thickness of, for example, from about 25 to about 250 microns.Among other considerations, the thickness of the dielectric layer islimited by the breakdown voltage of the material, which places a lowerlimit on the thickness. Thinner dielectric layers allow greater force tobe achieved. Also high dielectric constants are an advantage forcreating high force. If a gap exists between the wafer and chuck that isfilled either with a low pressure gas or a vacuum, then the dielectricconstant is essentially that of free space ∈_(o). It should also benoted that the dielectric layer may be a duplex structure using morethan one material. For example, as discussed further below, an aluminadielectric about 100 microns thick may be coated with a silicon carbidelayer about 2 microns thick, with protrusions from that surface, alsosilicon carbide, of 6 microns height.

As disclosed in U.S. Pat. No. 6,835,415, if the mounting surfaces of thetools allow any particulates to become entrapped between the mountingsurface and a substrate such as a wafer or mask, then the wafer or maskmay be deformed by the entrapped particle. For example, if a wafer isclamped, by vacuum or electrostatically, against a flat referencesurface, any entrapped particles could cause a deformation of the frontside of the wafer, which will therefore not lie in a flat plane. Thiscan cause variation in implant processes and potential yield loss.Reducing the contact area of the protrusions can reduce the probabilityof trapping particulates.

In accordance with an embodiment of the invention, the gas introducedinto the spaces between the substrate and the electrostatic chuck mayprovide sufficient thermal heat transfer to control the substratetemperature. At the same time, the gas pressure may be chosen to be lowenough that the attractive force holding the substrate to theelectrostatic chuck is not significantly diminished or overcome. Thethermal conductivity of a gas is essentially independent of gas pressureas long as the mean free path of the gas molecules is small compared tothe system dimensions. Cooling gases useful in accordance with anembodiment of the invention may include hydrogen, helium, argon,nitrogen, and mixtures of these and/or other gases. The back side gaspressures may be within the range of approximately greater than 0 torrto 20 torr, or in the range of about 2 torr to 15 torr. Further, inaccordance with an embodiment of the invention, the temperature of thechucked substrate may be controlled by gas heat conduction by adjustingthe back side gas pressure.

In accordance with an embodiment of the invention, discussed withreference to the embodiment of FIG. 2, an electrostatic chuck mayinclude a dielectric layer 212, which includes one or more protrusions201, overlying a first layer 214 that is insulating and may be a ceramicor ceramic composite. One or more electrodes 213 are embedded in thefirst layer 214 and covered with a dielectric, an amorphous dielectric,or a low stress dielectric material. One or more additional layers maybe included in the electrostatic chuck that provide mechanical supportto the first layer 214 and overlying dielectric 212, that aid in theremoval of heat, and that may contact a cooling fluid, such as water.The dielectric layer 212 may, for example, be a low stress siliconcontaining dielectric. The low stress dielectric may be amorphous andvapor deposited, for example by PECVD at low temperatures. Thedielectric layer 212 may have a thickness of, for example, from about 1micrometer to about 50 micrometers, or from about 1 micrometer to about10 micrometers. The first layer 214 is insulating and may be a ceramic,such as but not limited to alumina or aluminum nitride. The first layer214 may have a thickness of, for example, from about 50 micrometers toabout 200 micrometers, or from about 100 micrometers to about 150micrometers. The thickness of the dielectric layers can be used tocontrol the chucking force as described herein, with thinner layersproviding a greater force. Techniques of forming a patterned electrode213 of the kind described above are taught in U.S. Pat. No. 4,184,188 ofBriglia, which is incorporated herein by reference in its entirety.Electrical connections (feedthrough) through one or more layers of theelectrostatic chuck between the electrodes and external power supply areprovided (not shown). Gas inlets may also be formed through one or morelayers of the electrostatic chuck (not shown) with openings to thedielectric gap surface bottom. A first thermally conductive material orfirst adhesive layer 215 may be used to bond the first layer 214 with anunderlying second layer 216, which can be a ceramic or a metal. Thethermally conductive material of the first adhesive layer 215 may be anadhesive, such as but not limited to a thermoplastic, an epoxy, oranother material that can bond together the first layer 214 and thesecond layer 216. The second layer 216 may provide mechanical supportand thermal conductance and may be a ceramic, metal or other suitablematerial. Optionally a second thermally conductive layer or secondthermally conductive adhesive layer 217 bonds together the second layer216 and a bottom layer 218 that contacts a cooling fluid. The gap 211and optional gas channels can be filled with a gas, such as dry air,helium, hydrogen, argon or nitrogen. A gas seal 219 helps preventleakage of gas into the surrounding chamber.

With reference to the embodiment of FIG. 3, a cross-sectional view of anannular gas seal 319 and five protrusions 301 from a portion of thesubstantially equally spaced pattern of protrusions across theelectrostatic chuck are shown in that figure. Each protrusion 301 is araised surface of contact area. In one embodiment, the protrusions 301are cylindrical and have a diameter within a range of approximately 0.5millimeters to 1.25 millimeter, or of approximately 0.75 millimeters to1 millimeter. A substrate 200 such as a wafer (see the embodiment ofFIG. 2) contacts the dielectric 312 along the top surfaces 324 of theprojections 301 which can optionally be roughened. Although theprotrusions 501, 801 shown in the top views of the embodiments of FIGS.5 and 8 are circular, it should be understood that the protrusions 301,501, 801 can be in any shape, for example triangular, rectangular, orother shape that reduces particles due to non-uniform loading of thesubstrate on the protrusions.

In accordance with an embodiment of the invention, in order to containthe back side gas, a continuous annular ring can be formed at theperiphery of the electrostatic chuck to provide a gas seal between thesubstrate and chuck. The gas seal may be a continuous circular- orfeature-shaped ring at the interface between the chuck and thesurrounding vacuum, and may act to hold gas behind the wafer withminimal gas leakage. The annular ring may have a slightly smallerdiameter than the wafer to accommodate wafer placement tolerances, sothat if the wafer is misplaced the gas seal is not breached. Wherepossible the gas seal structure provides uniform distribution of forcebetween the substrate and chuck. In one embodiment, the gas seal mayinclude portions of protrusions in order to provide uniform distributionof force. The gas conductance of the annular gas seal(s), gas inlet gasseals, and lift pin gas seals(s) depends on the roughness of the contactsurfaces that create the gas seal, for example the roughness of thesurface of annular ring and the roughness of the surface of the waferthat contacts annular ring. Another factor that can affect the gas sealconductance is the presence of hard particles on the contact surfacesthat create the gas seal. The magnitude of the clamping force betweenthe contact surfaces that create the seal also effects the sealconductance. In accordance with an embodiment of the invention, a lowstress dielectric reduces or eliminates cracks and other surface defectsthat can provide particles and leak paths for various gas seals. In oneembodiment, an annular gas seal provides a leak rate of about 0.5 sccmor less at a chamber pressure for example but not limited to about 10⁻⁶torr to about 10⁻⁷ torr, a back side cooling gas pressure of for examplebut not limited to 4 torr to 15 torr, for a 200 millimeter wafer ofroughness of about 10 nanometers (nm) R_(a), a gas seal roughness of forexample but not limited to about 200 nm to about 300 nm R_(a), apotential difference of for example but not limited to 1000 volts acrossthe substrate and electrode.

EXAMPLE 1

This example illustrates calculated forces for a trigonal pattern of 6micron high bumps or protrusions, formed on the surface of anelectrostatic chuck in accordance with an embodiment of the invention.As shown in the embodiment of FIG. 8, on example includes protrusions801 that feature a 4 millimeter center to center spacing 827 and adiameter 828 of 0.75 millimeters. In the embodiment of FIG. 8, theprotrusions 801 may be made from 10 micron thick SiC vapor depositedfrom Si and C sources by PECVD on an alumina dielectric layer. The SiChas a low stress. The SiC layer may be etched by reactive ion etchingthrough a 30 micron photomask to form the protrusions. Gas seal ringsmay be formed around the perimeter of the electrostatic chuck, andaround the lift and ground pin holes of the electrostatic chuck. Gasports for adding and removing a gas, such as helium or hydrogen oranother fluid for gas heat transfer may be formed in the chuck.

FIG. 6 is a graph of calculated force between a wafer and electrostaticchuck protrusions for various protrusion diameters and center to centerbump spacing, in accordance with an embodiment of the invention. Thecalculated values assumes a load uniformly distributed over theprotrusion surface; however, it is also possible to calculate the forceusing percent loadings to account for wafer lift (for example 10%, 20%,27% or other portion of force due to edge loading). The results showthat 0.75 mm and 1 mm diameter protrusions in a trigonal pattern resultin lower force between the substrate and protrusions than similarprotrusions having a 0.25 mm or 0.5 mm diameter. The results also showthe non-linear relationship between protrusion spacing and force, andthe non-linear relationship between protrusion diameter and force. As aparticular example, the distributed average force for the protrusions801 of the embodiment of FIG. 8 may be compared with the forces forother protrusions using the graph of FIG. 6. The 0.75 mm protrusions 801of the embodiment of FIG. 8 are about 50% larger compared to 0.5 mmprotrusions and result in an approximately eight times lower distributedaverage force, as shown in FIG. 6, compared to a square pattern ofprotrusions spaced 8 mm apart and having a diameter of 0.5 mm, for whichthe calculated force is indicated by a star in FIG. 6. The 0.75 mmprotrusions of the embodiment of FIG. 8 are about 50% larger compared to0.5 mm protrusions and result in an eight times higher contact area. Thecontact area for the protrusions 801 of the embodiment of FIG. 8 may beless than or equal to 4% and greater than 1%. This range providesreduced average force between the wafer and protrusions and less waferbowing, while maintaining a 25-35 torr wafer holding force (clampingforce) and is expected to have no significant effect on the coolingefficiency of the wafer.

FIG. 7 is a graph of calculated contact area for different protrusiondiameters and center to center protrusion spacings, in accordance withan embodiment of the invention. The arrow points to a calculated contactarea of 0.36% for a protrusion spacing of 0.5 mm and a square pattern ofprotrusions.

EXAMPLE 2

This example describes a trigonal pattern of protrusions that was formedon the surface of an electrostatic chuck, with 8 millimeter center tocenter spacing between protrusions in accordance with an embodiment ofthe invention. The diameter of the protrusions was 0.5 millimeters. Theprotrusions on the platen of the electrostatic chuck were divided intothree sections and made from different materials (SiC, anon-stoichiometric SiC deficient in carbon, and an Si section). Theindividual sections were made by PECVD of suitable precursor gasesdeposited on an alumina dielectric layer. The sections were etched byreactive ion etching through a 30 micron photomask to form theprotrusions. Gas seal rings may be formed around the perimeter of theelectrostatic chuck and around the lift and ground pin holes of theelectrostatic chuck. Gas ports for adding and removing a gas, such ashelium or hydrogen or another fluid for gas heat transfer, may be formedin the chuck.

FIGS. 9A and 9B are graphs of a cross-sectional profile of a protrusionon an electrostatic chuck with and without (FIGS. 9A and 9Brespectively) an added stage of machine polishing, in accordance with anembodiment of the invention. In this embodiment, it has been recognizedthat adding an additional stage of machine polishing of the top surfaceof a protrusion provides significant unexpected performance benefits byreducing particle production, and results in 1) a different protrusionedge geometry; and 2) a significantly improved surface roughness. Moreparticularly, a production process without added machine polishing useshand polishing only, for example by polishing the top surface of anelectrostatic chuck protrusion by hand with 600 grit silicon paper. Aprofile of the resulting protrusion is shown in FIG. 9A, in accordancewith an embodiment of the invention. As can be seen, the profile of thetop surface 929 features some roughness. In addition, the edge geometryindicates a relatively long rounding height dimension 930, with arelative short rounding length dimension 931. In an improved embodiment,the hand polishing of the protrusion is supplemented with machinepolishing, for example using machine pad polishing. Such machine padpolishing may be performed at a specified pressure for a specified time.Further, machine polishing may include lapping, such as use of a lappingmachine in a polishing mode, and may include use of a soft or hardpolishing pad, with use of any suitable polishing media such aspolishing media that includes diamond. A profile of the resultingprotrusion is shown in FIG. 9B, in accordance with an embodiment of theinvention. It will be seen that the profile of the top surface 932 issmoother by comparison with the roughness 929 of the hand polishedprotrusion of FIG. 9A. Further, the protrusion of FIG. 9B features amodified edge geometry, with a shorter rounding height dimension 933 bycomparison with the corresponding height 930 of FIG. 9A, and a longerrounding length dimension 934 by comparison with the correspondingheight 931 of FIG. 9B.

Thus, the machine pad polishing of the embodiment of FIG. 9B providesboth a reduced surface roughness and a modified edge geometry bycomparison with a protrusion that is only hand polished. For example, inone embodiment, the machine pad polished protrusion of FIG. 9B may showabout a 50% reduction in a surface roughness metric, such as R_(a),which is a measure of average of roughness height, by comparison withsuch a metric for a hand polished protrusion. The reduction may be, forexample, from a surface roughness of about 100 nm to about 50 nm.

FIGS. 10A and 10B are close-up graphs of the cross-sectional profiles ofthe protrusions of FIGS. 9A and 9B, respectively, in accordance with anembodiment of the invention. It can be seen that, as a result of themachine pad polishing of the protrusion of FIG. 10B, the peaks 1035 ofthe machine pad polished protrusion of FIG. 10B are lower than the peaks1036 of the hand polished protrusion of FIG. 10A (although the troughsmay not be affected), so that an overall surface roughness metric, suchas R_(a), is reduced. For example, the surface roughness R_(a) may bereduced from about 0.10 μm in FIG. 10A to about 0.04 μm in FIG. 10B.More generally, a surface roughness metric may be reduced by about 50%,or by between 25% and 75%, by machine pad polishing of the surface of aprotrusion. Further, by virtue of the machine pad polishing, there maybe observed a modified edge geometry of the protrusion, such as ashorter rounding height dimension by comparison with the correspondingheight of a similar hand polished protrusion, and a longer roundinglength dimension by comparison with the corresponding length of asimilar hand polished protrusion. For example, a ratio of acharacteristic rounding height dimension to a characteristic roundinglength dimension of the edge of the protrusion may be reduced by afactor of, for example, between 3 and 4, such as a reduction from aratio of 0.01222 to a ratio of 0.0034 (i.e., in that case, a ratioreduced by a factor of roughly 3.59) for a height/length of 0.7802μm/0.0638 mm when polished only by hand as compared with 0.3525μm/0.1035 mm when machine pad polished; or by a factor between 2 and 5.It should be noted that a similarly modified edge geometry may also beobtained without machine polishing. In one embodiment, a modified edgegeometry such as that of FIG. 10B, which features a relatively shorterrounding height dimension and a relative longer rounding lengthdimension, may be achieved by any edge-modification technique to producethe desired rounding height to rounding length ratio. For example, aratio of a characteristic rounding height dimension and a characteristicrounding length dimension of between about 0.00407 and about 0.00306, orbetween about 0.00611 and about 0.002444, may be used.

In addition, by virtue of the machine pad polishing of a protrusion inaccordance with an embodiment of the invention, an electrostatic chuckmay have an improved performance by producing fewer back side particlesin use with a substrate, such as a semiconductor wafer. For example,fewer than 5000 particle adders, or fewer than 2000 particle adders, maybe generated in a particle size range of 0.16 μm or greater. Such areduced production of back side particles may be accompanied by a lackof impact on thermal characteristics, even with an increase in contactarea between protrusions and substrate, such as an increase of up to tentimes in contact area.

FIG. 11 shows an electrostatic chuck that includes a charge controlsurface layer, according to an embodiment of the invention. In thisembodiment, a surface layer having a controlled surface resistivity isused to reduce the likelihood of “wafer sticking,” which occurs when awafer or other substrate electrostatically adheres to the chuck surfaceafter the chuck power is removed. A surface layer having a surfaceresistivity in an appropriate range, such as, for example, a range offrom about 1×10⁸ ohms/square to about 1×10¹¹ ohms/square, has been shownto reduce surface charge retention that can lead to undesirableelectrostatic force and ultimately to wafer sticking. The slightlyconductive surface layer bleeds charge to ground (not shown) while notinterfering with the electrostatic attraction between the electrostaticchuck and the substrate.

The electrostatic chuck of the embodiment of FIG. 11 has been tested inan ion implant machine with good results for wafer cooling and clampforce, and with low particle generation and minimal wafer damage. Inparticular, there was less than a 50° C. rise in temperature of theplaten from the 1800 watts power incident on the platen from the ionimplant beam, and after testing, less than 5000 adders of a size greaterthan 0.12 microns were found on the platen. Because of the materialsused to make the protrusions, in particular a silicon carbide coating,and the intrinsic controlled bulk resistivity of the coating, waferswere less likely to electrostatically adhere to the chuck surface afterthe chuck power was removed.

In the example of the embodiment of FIG. 11, the wafer contact surfacewas built on a 300 mm diameter Coulombic-type chuck that employedalumina ceramics for the insulator and dielectric materials. A six-phasealternating current power supply was used to charge and discharge thechuck in a manner described in U.S. Pat. No. 6,388,861, the contents ofwhich are incorporated herein by reference. Specifically, as describedat Col. 4, line 66 through Col. 5, line 23 of U.S. Pat. No. 6,388,861,the chuck includes six electrodes, and bipolar square wave clampingvoltages having six different phases are applied to the electrodes. Itwill be appreciated that other power supplies (such as DC powersupplies) and techniques for charging and discharging the chuck may beused. The electrostatic chuck surface includes gas inlets 1137, a groundpin passage 1138, a gas seal ring 1119, a lift pin passage 1139 thatincludes its own gas seal ring (outer light-colored structure of liftpin passage 1139 in FIG. 11), and a small gas inlet at 1140 in thecenter of the chuck (inlet not visible in FIG. 11). A detail view (inset1141 in FIG. 11) shows the protrusions 1101.

FIG. 12 shows the surface pattern used for the protrusions 1201 in theelectrostatic chuck of the embodiment of FIG. 11. The protrusions 1201were made in a triangular pattern with a center-to-center spacing 1228of 4 mm and a diameter 1227 of 800 microns (0.8 mm). The protrusions1201 had a height 1326 (see FIG. 13) of 5 to 7 microns, which isconsidered optimum for operation with back side gas of 15 torr pressure.The controlled surface resistivity layer was a silicon carbide coatingproduced by a plasma assisted physical vapor deposition (PACVD) process,although other suitable processes may be used. For example, the layermay also be deposited by physical vapor deposition (PVD) (sputteringfrom a SiC target or reactively sputtered from a silicon target in acarbon reactive gas), atomic layer deposition (ALD), high temperatureCVD or other thin film methods.

The protrusions 1201 were made by blanket depositing a silicon carbidecomposition, such as silicon carbide or non-stoichiometric siliconcarbide, on the flat alumina dielectric 1312 (see FIG. 13), patterningthe silicon carbide composition using photolithography, and thenremoving portions of the silicon carbide composition with reactive ionetching to leave the protrusions 1301 (see FIG. 13). The resistivity ofthe silicon carbide composition (which may be either silicon carbide ornon-stoichiometric silicon carbide) was controlled by varying the amountof silicon precursor gas and carbon precursor gas used to make thesilicon carbide composition and to achieve silicon carbide ornon-stoichiometric silicon carbide with a surface resistivity in therange of from about 1×10⁸ ohms/square to about 1×10¹¹ ohms/square. Forexample, the composition of the silicon carbide composition may bevaried by adjusting the flow rates or ratios of silicon- andcarbon-containing precursor gases that are input into a reactor of aplasma-enhanced CVD process. The precursor gases decompose and form acoating on the electrostatic chuck, with the composition of the siliconcarbide coating being determined by the relative flow rates or ratios ofthe precursor gases. The surface resistivity of the coating can bevaried by varying the composition of the coating.

Other low stress coatings with the same surface resistivity range couldbe similarly deposited on the alumina and patterned. For example,coatings with an internal compressive film stress of less than about 450MPa, and more preferably less than about 450 MPa (as deposited) may beused. Further, the coatings may be formed with a low stress material(such as one with an internal compressive film stress in a range of lessthan about 450 MPa), and then overcoated with a thin coating ofdiamond-like carbon (or other material that typically has a highercompressive film stress) to achieve the desired surface resistivity.FIG. 13 is a schematic cross-sectional view of the substrate contactsurface of the embodiment of FIG. 11. The dielectric material 1312 isalumina, and the protrusion 1301 material is silicon carbide, which ischosen for its high hardness and adjustable bulk resistivity. Thesilicon carbide protrusion 1301 and coating layer 1342 has a bulkresistivity of about 1×10⁸ ohm-cm, which results in a surfaceresistivity of about 1×10¹⁰ ohms per square. Surface resistivity in therange of from about 1×10⁸ ohms/square (made using a non-stoichiometricsilicon carbide composition that is richer in carbon) to about 1×10¹¹ohm/square (made using a non-stoichiometric silicon carbide compositionthat is richer in silicon) has been shown to reduce surface chargeretention that can lead to undesirable electrostatic force andultimately wafer sticking. The coating layer 1342 can be from about 0.1to about 10 microns thick, but is preferably from about 1 to about 3microns thick. A center-to-center spacing 1328 of 4 mm is shown, butother spacings may be used.

Another feature of the electrostatic chuck of the embodiment of FIG. 11is a continuous ring 1119 (see FIG. 11) of silicon carbide at the sameheight from the chuck plane as the protrusions that circles the entirechuck at the edge and also circles the larger through holes in thecenter of the chuck. These rings act to contain the back side gas whenthe wafer is electrostatically attracted to the surface.

FIG. 14 shows an alternative version of the coating for theelectrostatic chuck of FIG. 11 in which a conformal coating 1442 ofcharge control material is used, in accordance with an embodiment of theinvention. The alumina dielectric 1412 (electrodes not shown) can bepatterned first by bead blasting or by using an etching technique toform protrusions 1401, gas seals and the like. The dielectric 1412 canthen be coated, essentially conformally, with the silicon carbide orother charge control material layer 1442 that has a surface resistivityin the range of from about 1×10⁸ ohms/square to about 1×10¹¹ohms/square. The embodiment of FIG. 14 may have the advantage of lowermanufacturing cost than that of FIG. 13. A protrusion height 1426 of 5to 7 microns and spacing 1428 of 4 mm is shown, but other protrusionheights and spacings may be used.

In accordance with the embodiments of FIGS. 11-14, a surface resistivityin the range of from about 1×10⁸ ohms/square to about 1×10¹¹ ohms/squareis preferable for the charge control surface layer 1301/1342, 1442.Preferably, the charge control surface layer should be a non-parasiticconductive layer, since a parasitic conductive layer would undesirablycouple the electrostatic force of the electrostatic chuck to the chargecontrol surface layer rather than to the substrate. By keeping thesurface resistivity of the charge control surface layer in the range offrom about 1×10⁸ ohms/square to about 1×10¹¹ ohms/square, theelectrostatic force of the electrostatic chuck is coupled to thesubstrate rather than to the surface layer itself. If the surface layerhas a surface resistivity that is either too far above or too far belowthis range, there is a risk of either a reduction in clamping force ofthe electrostatic chuck, or of insufficient charge bleeding from thesurface of the chuck and an increased tendency for wafer sticking tooccur.

Other materials than silicon carbide compositions may be used to formthe charge control surface layer, in accordance with an embodiment ofthe invention. For example, diamond-like carbon, amorphous silicon,metal-doped oxides or other materials may be used. Preferably, thecharge control surface layer should have a surface resistivity in therange of from about 1×10⁸ ohms/square to about 1×10¹¹ ohms/square,regardless of the material used. The material used for the chargecontrol surface layer should be thermally and chemically stable, whilealso having a surface resistivity in the appropriate range. A surfaceresistivity range of from about 1×10⁶ ohms/square to about 1×10¹⁰ohms/square could be achieved with diamond-like carbon, for example,although preferably a range of from about 1×10⁸ ohms/square to about1×10¹¹ ohms/square should be used. Diamond-like carbon can preferably beused with the manufacturing technique of FIG. 13, in which blanketdepositing is used; and is preferably used in a thin layer. Generally,for a given bulk resistivity material, a thinner layer produces a highersurface resistivity and vice versa. In general, the composition andthickness of the charge control surface layer should be adjusted toachieve the appropriate surface resistivity.

In accordance with an embodiment of the invention, use of anelectrostatic chuck can include the acts or steps of chucking,de-chucking, performing a microelectronic manufacturing process on achucked wafer, and combinations including any of these.

It should be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural reference unless thecontext clearly dictates otherwise. Thus, for example, reference to a“protrusion” is a reference to one or more protrusions and equivalentsthereof known to those skilled in the art, and so forth. Unless definedotherwise, all technical and scientific terms used herein have the samemeanings as commonly understood by one of ordinary skill in the art.Methods and materials similar or equivalent to those described hereincan be used in the practice or testing of embodiments of the presentinvention. All publications mentioned herein are incorporated byreference in their entirety. Nothing herein is to be construed as anadmission that the invention is not entitled to antedate such disclosureby virtue of prior invention. “Optional” or “optionally” means that thesubsequently described event or circumstance may or may not occur, andthat the description includes instances where the event occurs andinstances where it does not. All numeric values herein can be modifiedby the term “about” or “substantially” whether or not explicitlyindicated. The term “about” or “substantially” generally refers to arange of numbers that one of skill in the art would consider equivalentto the recited value (i.e., having the same function or result). In someembodiments the term “about” or “substantially” refers to ±10% of thestated value, in other embodiments the term “about” or “substantially”refers to ±2% of the stated value. While compositions and methods aredescribed in terms of “comprising” various components or steps(interpreted as meaning “including, but not limited to”), thecompositions and methods can also “consist essentially of” or “consistof” the various components and steps. “Consist essentially of” or“consist of” should be interpreted as defining essentially closed-membergroups.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. An electrostatic chuck comprising: an electrode;and a surface layer activated by a voltage in the electrode to form anelectric charge to electrostatically clamp a substrate to theelectrostatic chuck, the surface layer including: (i) a dielectriccomprising a resistivity greater than about 10¹² ohm-cm such that theelectrostatic chuck is a Coulombic chuck; and (ii) a charge controlsurface layer coating overlying the dielectric and comprising athickness in the range of from about 0.1 microns to about 10 microns anda surface resistivity in the range of from about 1×10⁸ ohms/square toabout 1×10¹¹ ohms/square, the charge control surface layer coatingfurther comprising a plurality of protrusions extending to a heightabove portions of the surface layer surrounding the protrusions tosupport the substrate upon the protrusions during electrostatic clampingof the substrate, the protrusions being substantially equally spacedacross the surface layer as measured by a center to center distancebetween pairs of neighboring protrusions, the protrusions comprising alow stress material having an internal compressive film stress less thanabout 450 MPa and comprising an overcoating of diamond like carbon; thecharge control surface layer comprising a surface coating layercomprising portions of the surface layer surrounding the protrusions,above which the protrusions extend; and wherein the protrusions includemodified edge geometry such that a ratio of a characteristic roundingheight of a protrusion to a characteristic rounding length is equal to agiven ratio, wherein the given ratio is between about 0.00611 and about0.002444.
 2. An electrostatic chuck according to claim 1, wherein theprotrusions are arranged in a trigonal pattern.
 3. An electrostaticchuck according to claim 2, wherein the protrusions have a diameter offrom about 0.75 millimeters to about 1 millimeter, and wherein thecenter to center distance between pairs of neighboring protrusions isless than about 8 millimeters.
 4. An electrostatic chuck according toclaim 1, wherein at least one of the height and a contact area androughness of the protrusions are such that at least one of thetemperature and the temperature distribution of the substrate, when thesubstrate is heated during the electrostatic clamping, is substantiallycontrolled by gas heat conduction of a gas in a space between thesubstrate, the protrusions, and the portions of the surface layersurrounding the protrusions.
 5. An electrostatic chuck according toclaim 1, wherein greater than a proportion of a top area of each of theprotrusions contacts the substrate during the electrostatic clamping,the proportion of the top area being selected from the group consistingof about 25%, about 50%, and about 75%.
 6. An electrostatic chuckaccording to claim 1, wherein less than a number of particle adders aredeposited on a back side of the substrate as a result of a use of theelectrostatic chuck that includes at least one of: the electrostaticclamping of the substrate, de-clamping the substrate from theelectrostatic clamping, and performing the electrostatic clamping duringa manufacturing process performed on the substrate; the number ofparticle adders being selected from the group consisting of: about 5000particle adders; about 3000 particle adders; about 2500 particle adders;and about 1500 particle adders.
 7. An electrostatic chuck according toclaim 1, wherein the low stress material comprises at least one of anamorphous dielectric material and a polycrystalline dielectric material.8. An electrostatic chuck according to claim 1, wherein the protrusionscomprise a dielectric material having a resistivity greater than about10¹² ohm-cm.
 9. An electrostatic chuck according to claim 1, wherein theprotrusions comprise a dielectric material including at least one of:silicon, an alloy of silicon with at least one other element, siliconcarbide and non-stoichiometric silicon carbide.
 10. An electrostaticchuck according to claim 1, wherein the protrusions comprise adielectric material including at least one of alumina and aluminumnitride.
 11. An electrostatic chuck according to claim 1, wherein theprotrusions comprise a compliant dielectric material.
 12. Anelectrostatic chuck according to claim 1, wherein a contact area of theprotrusions with the substrate comprises from about 1% to about 10% of atotal area of the electrostatic chuck.
 13. An electrostatic chuckaccording to claim 1, wherein the protrusions have a diameter of fromabout 0.75 millimeters to about 1 millimeter.
 14. An electrostatic chuckaccording to claim 1, wherein the center to center distance betweenpairs of neighboring protrusions is less than about 8 millimeters. 15.An electrostatic chuck according to claim 1, wherein the center tocenter distance between pairs of neighboring protrusions is less than adistance, wherein the distance is selected from the group consisting of:about 6 millimeters, about 4 millimeters, and about 2 millimeters. 16.An electrostatic chuck according to claim 1, wherein the protrusionscomprise at least one partial protrusion, the partial protrusioncomprising at least part of a surface structure of the electrostaticchuck.
 17. An electrostatic chuck according to claim 16, wherein thesurface structure is selected from at least one of a gas channel, a liftpin and a ground pin.
 18. An electrostatic chuck according to claim 1,wherein the height of the protrusions is substantially equal to the meanfree path of a gas located during the electrostatic clamping in a spacebetween the substrate, the protrusions, and the portions of the surfacelayer surrounding the protrusions.
 19. An electrostatic chuck accordingto claim 1, wherein the protrusions include a top surface having asurface roughness metric reduced, by virtue of at least some machinepolishing, by between about 25% and about 75% by comparison with similarprotrusions polished only by hand.
 20. An electrostatic chuck accordingto claim 19, wherein the surface roughness metric is reduced by about50%.
 21. An electrostatic chuck according to claim 20, wherein less thanabout 2000 particle adders of particle size range of 0.16 μm or greaterare deposited on the back side of the substrate as a result of the useof the electrostatic chuck.
 22. An electrostatic chuck according toclaim 19, wherein less than about 5000 particle adders of particle sizerange of 0.16 μm or greater are deposited on the back side of thesubstrate as a result of the use of the electrostatic chuck.
 23. Anelectrostatic chuck according to claim 19, wherein less than about 2000particle adders of particle size range of 0.16 μm or greater aredeposited on the back side of the substrate as a result of the use ofthe electrostatic chuck.
 24. An electrostatic chuck according to claim1, wherein the protrusions include modified edge geometry produced by atleast some machine polishing, such that a characteristic rounding heightof a protrusion is shorter by comparison with a corresponding height ofa similar protrusion polished only by hand and such that acharacteristic rounding length is longer by comparison with acorresponding length of a similar protrusion polished only by hand. 25.An electrostatic chuck according to claim 24, wherein the ratio of thecharacteristic rounding height to the characteristic rounding length isreduced by a factor by comparison with the similar protrusion polishedonly by hand, wherein the factor is selected from the group consistingof: between about 2 and about 5; and between about 3 and about
 4. 26. Anelectrostatic chuck according to claim 1, wherein the charge controlsurface layer comprises a silicon carbide composition.
 27. Anelectrostatic chuck according to claim 26, wherein the surfaceresistivity of the charge control surface layer is controlled by varyingthe amount of silicon precursor gas and carbon precursor gas used tomake the silicon carbide composition.
 28. An electrostatic chuckaccording to claim 26, wherein the silicon carbide composition comprisessilicon carbide.
 29. An electrostatic chuck according to claim 26,wherein the silicon carbide composition comprises non-stoichiometricsilicon carbide.
 30. An electrostatic chuck according to claim 1,wherein the charge control surface layer is formed by: blanketdepositing a silicon carbide composition layer on a dielectric;patterning the silicon carbide composition layer using photolithography;and removing portions of the silicon carbide composition layer usingreactive ion etching to leave at least one silicon carbide compositionprotrusion.
 31. An electrostatic chuck according to claim 1, wherein thecharge control surface layer is formed by: patterning a dielectric layerusing bead blasting or etching; and conformally coating the dielectriclayer with the charge control surface layer.
 32. An electrostatic chuckaccording to claim 1, wherein the charge control surface layer comprisesat least one material selected from the group consisting of diamond-likecarbon, amorphous silicon, metal-doped oxide and combinations of these.33. An electrostatic chuck according to claim 1, wherein the chargecontrol surface layer comprises a thickness in the range of from about 1microns to about 3 microns.
 34. An electrostatic chuck according toclaim 1, wherein the dielectric comprises a thickness in the range offrom about 25 microns to about 250 microns.
 35. An electrostatic chuckaccording to claim 1, wherein the charge control surface layer comprisesa silicon carbide composition, and wherein the charge control surfacelayer comprises a thickness in the range of from about 1 microns toabout 3 microns.
 36. An electrostatic chuck according to claim 1,wherein the given ratio is between about 0.00407 and about 0.00306. 37.An electrostatic chuck according to claim 1, wherein the protrusionsinclude a top surface having a peak to valley surface roughness of 2microns R_(a) or less.